Noninvasive estimation of FDG input function for quantification of cerebral metabolic rate of glucose: Optimization and multicenter evaluation

The aims of this study were to determine whether body weight or body surface area (BSA) should be used for noninvasive measurement of the cerebral metabolic rate of glucose (CMRGIc) by FDG PET with a standardized input function (SIF) and an autoradiographic method and to validate the procedure in a large population from different PET centers. Methods: Plasma input functions measured by intermittent arterial blood sampling after intravenous injection of FDG, in 101 patients from 1 institution who were fasting for at least 4 h, were used to generate the SIF. The SIF was generated by averaging over 101 patients the input function normalized with the net injected dose and initial distribution volume (DV) of FDG estimated by the formula c x H-a X W-b, where H is body height and W is body weight. To evaluate the estimation of DV by BSA or body weight, the coefficient of variation (CV) of the ratio of Ha X Wb to the measured DV was calculated by changing a and b independently. Estimation of the CMRGIc with SIF based on the formula for DV was validated with an additional 192 subjects from 3 institutions who underwent FDG PET while fasting. The result of simulation was compared with the results of 4 previously published formulas for BSA and body weight. Results: The optimal set of parameters, in which a was 0.80 and b was 0.35, minimized the CV. The averaged percentage error of the CMRGIc based on the optimal set of parameters for DV estimation and SIF was 8.9% for gray matter and 10.6% for white matter. Four BSA formulas brought about a similar error, which was significantly smaller than that based on body weight (P < 0.001, ANOVA). Conclusion: Noninvasive estimation of CMRGIc is made possible by careful measurement of the net injected dose and BSA.